Electrical indicator



(No Model.) 2 sheets-sheen 1. C. -WIRT.

ELECTRICAL INDICATOR.

1\To.-31=5,'755a Patented July 20, 1886,

(N0 Model.) I 2 Sheets-Sheet 2.

C. WIRT.

ELECTRICAL INDIGATOR.

No. 345,755. Patented Ju1y20, 1886.

UNITED STATES PATENT CEEICE.

CHARLES VIRT, OF CI-IIGAGO, ILLINOIS.

ELECTRICAL INDICATOR.

SPECIFICATION forming part 0I' Letters Patent Nvo. 345,755, dated July20, 1886.

Application filed Octub( r 2, 1385.

To all whom, it 11i/ay concern:

Be it known that I, CHARLES WIRT, of Chicago, in the county of Cook andState of Illinois, have invented a certain new and useful Improvement inElectrical Indicators, of which the following is a specification.

My invention relates to an instrument or apparatus for measuring theelectro-motive force existing at any part of an electric circuit.

The instrument consists, essentially, of a graduated variableresistance, and a shunt around a part of said resistance, including astandard battery, a galvanometer, and a circuit making and breaking key.The resistance is connected between the two points whose difference ofpotential it is desired to measure. 'NVhen the key is closed, thestandard electro-motive force of the battery is opposed by theelectro-motive force of that portion of the circuit whose electro-motiveforce is to be measured, and if these two are equal thegalvanometenneedle will remain at rAero, there being no current in theshunt. If, however, one electro-motive force is greater than the other,the needle will be deiiected. rlhe variable resistance is then adjusteduntil the needle returns again to zero, when the electromotive force isknown by the resistance in circuit, the resistancesections beinggraduated so as to indicate this,as will be explained.

My invention further consists in the novel devices and combinations ofdevices employed by me in carrying out the principle of operation justexplained, as hereinafter set forth and claimed.

In the accompanying drawings, Figure 1 is a perspective view of acomplete instrument embodying my invention; Fig. 2, a diagramillustrating the principle of the invention, Fig. 3, a top View of theinstrument with diagram of the connections; Fig. 4, a View of the keywhich I prefer to employ, and Fig. 5 a section of the galvanometer.

Referring rst to Fig. 2, A B represent a Variable series of resistancesconnected across the circuit the electromotive force in which it isdesired to indicate. In a shunt around a portion, G D, ofthe resistancesare astandard battery, S, a galvanometer, G, and akey, K. In theresistance-circuit is a circuit-re- Seriul Nu. 178,853. (No model.)

'vel-sing switch, R. Vhen the key is closed,

the battery-current opposes the main current in C D, and theelectro-motive forces are in the following proportions: Theelectro-motive force from A to Bis to the opposing standardelectro-motive force as the resistance from A to Bis to the resistancefrom C to D. The ratio ofA B andC D is altered by Varying the number ofresistance-coils in circuit. It' the galvanometer is deliected when thekey is closed, then the resistance A Bin circuit is decreased orincreased until it again stands at zero. Then the total of the nominalvalues of resistance A B in circuit represent the elec-A tro-motiveforce from A to B.

Referring to Figs. l, 3, 4, and 5, E E are two wooden boxes or framesmounted on a common base, F. Frame E supports within it theresistance-coils, which consist of insulated wire c a, coiled upon liatstrips b I), which are held in slots c o. These coils are connected byconnections through the top of the fra-me with plates d cl2-as shown inFig. 8, so that the insertion of a plug between two plates cuts out ofcircuit that portion of the resistance which is connected to thoseplates. The battery consists of three compartments, H H H, constructedand arranged as set forth in an application made by me of the same dateherewith, and is placed in a suitable case, I, in the space between thetwo frames E E. Frame E supports the galvanometer. The connections tothe galvanometer are so made as to permit the instrument to be turned soas to bring its needle to zero,`whereby the neces sity for usingexternal attraction for this purposeis done away with. Such connectionsare made by a curved spring, e, bearing on the circular metal case f ofthe galvanometer and carried by an arm, g, extending from bindingpostlL, and a curved spring, c', bearing on a metal ring, f', on theinsulating-bottom ofthe instrument and carried by an'arm, g', extendingfrom binding post h. From case f` and ring'f wires i and i extend,respectively, to the galvanometer-coils. The key in the shunt is adouble key. From its lower stationary contact, j, a wire, 7a, extends toa point, Z, on the adjustable resistance. From its lower circuitclosingstrip, m, Wire n extends to binding-post 0, from which wire p goes toone of the battery-terminals. From strip m Wire g goes to plate d of therheostat, and from m2 wire r goes to plate d2. The other terminal of thebattery is connected by Wire s with binding-post h. Plate d of therheostat is connected by wires t t with binding-post h. The double keycloses one circuit before the other, the extra contacts u beingprovided, so that m2 must make contact with m before the latter pushes mdown upon j, and so as to lessen contact resistance. m and m have aninsulating-button, e, between them. The connec- Ytions with the circuitwhose electro-motive force is to be determined is made throughconductors combined in a eXible cord, w, in any suitable manner. At theend of this cord is a connecting device, which consists of a body'ofinsulating material, x, having a crosspiece, y, which carries two metalpins or plugs, z z. The iexible cord enters and its conductors aretherein connected with z c. To make connection the pins are thrust intothe holes of the binding posts z2 z3 of the rheostat. .hen both contactsof the key are closed, the circuits are as follows: From z2 through suchresistances a as are in circuit to d2 by r, to m2 and m by q to d', andagain by cca to z3. This corresponds with circuit A B of Fig. 2. Theshunt is from Z to j m u o p to battery s t" to galvanometer, i t t tod3. The key (mj,) battery, andgalvanometerare thus shunted around aportion of the resistance, as represented by C D of Fig. 2.

The operationis as follows: Connection with the circuit having been madeas described, the galvanometer is first turned so as to bring itspointer to zero. Then the key is tapped and closes first theresistance-circuit and then the battery-shunt through a portion of saidresistance,so that the two currents are there opposed. 1t' theelectro-motive force of one is more than that of the other, the needlewill be slightly deflected.y Portions of resist-ance aa are then cut outof circuit until the needle again returns to Zero, whereupon theelectro-motivev force of the circuit under consideration is known, isdenoted by the amount of resistance which is in circuit. If, when thekey is first closed, the galvanometer is violently deflected, itindicates that the two currents are in the same direction. The plugs zzare then withdrawn, and the connecting device turned around so as to puteach plug in the other binding-post, and thus reverse the circuit. Thismay often occur in practice, as when the indicator is connected with thecircuit at a point where the direction of the current is not known. Itis therefore desirable to have a circuit-reverser of some kind, and thatabove described is a very simple and convenient form. I may, however,employ any other suitable device for the same purpose-such, forinstance, as the circuit-reverser R of Fig. 2.`

By means of the double key the resistancecircuit may be kept closedwithout closing the battery-circuit; or, if desired, theresistancecircuit may be closed by inserting a plug between d and d2.The binding-posts h and h are provided so that the galvanometer may beused for other work, if desired.

The use ofthe connecting device for the ilexible cord is not confined tothis apparatus alone. It is evident that such a device may be used inany case where a flexible cord is to be connected to binding-posts, andis advantageous over the usual practice of having two loose ends for theconductors, sinceY these are not unlikely to come in contact and producea short circuit when the cord is dropped from the binding-posts.

The resistance-coils are wound in single layers, and, being on fiatspools, there is little heating and little danger of a short circuitoccurring. The preferred way of forming the coils is to wind the wire onpaper tubes and then compress them into the tlat shape.

The whole apparatus is placed in an inclosing-box, (shown by dottedlines M M in Fig. 1,) and is thus conveniently transported from place toplace. The frames E E may be conveniently removed from the box, and thebattery-case also maybe readily taken out for rcfilling.

What I claim isl. In an electrical indicator, the combination of avariable resistance adapted to be connected across the two points of thecircuit at which its electro-motive force is to be determined, a shuntaround a definite portion of said resistance, means for producing acounter IOC electro-motive force in said shunt, and means f forindicating the current in said shunt, substantially as set forth.

2. In an electrical indicator, the combination of the variableresistance, the shunt including the standard battery, galvanometer, andkey, and a reverser for the resistance-circuit, substantially as setforth.

3. The combination of the supporting-frame provided with slots of theflat resistance-spools held by said slots, substantially as set forth.

4. The combination, with a galvanometer,-

of sliding contacts permitting the turning of the galvanometer,substantially as set forth.

5. The combination, with a galvanometer having a metal case and a metalring on its insulating-bottom, ofa contact-spring bearing on said case,a contact-spring on said ring, and connections from said case and saidring to the galvanometer-coils, substantially as set forth.

This specification signed and witnessed this 21st day of September,1885.

CHARLES W'IRT.

W'itnesses:

FRANK A. HELMER, ALBERT N. EAsTMAN.

IIC

